Distinguished

Yes it would make a nice improvement on gaming!!
But I would suggest something better then "some 450W one" for psu...
Quality brands are Corsair, Seasonic, Enermax, PCP&C, XFX and there are more so post anything that you might concider...

With such an expensive upgrade, you may wish to ask yourself if it's even worth it (if it's only for Crysis 3 I'd personally say no), and if so maybe you should spend a LITTLE MORE and get a better graphics card?

The above card has Crysis 3 and Bioshock Infinite included. Since it costs $290 (after MIR) the actual card costs LESS THAN $200.

HD7950 vs GTX660:
Performance is similar, but the benchmarks seem to indicate the HD7950 on average beats the GTX660. You'll have to look at the Pros and Cons more closely I guess as it's not completely cut and dry.